1. Field of the Invention
The invention relates to a process for rendering visible an electrostatic charge image, by deforming the surface of a liquid being present on a support into a reversible, optically readable relief image, and to an apparatus which is suitable for carrying out the process.
2. Description of the Prior Art
It is known, as illustrated, for example in U.S. Pat. No. 3,560,205 to produce a charge image directly on a thermoplastic layer by an image-wise electrostatic charging or, by utilizing an additional photoconductive layer, by electrostatic charging and exposure. When heated, the surface of the thermoplastic layer is deformed into a relief image which is rendered optically visible. In such processes, the heating step is a very critical process step since the optimum temperature range of such a layer is very small. The stability of the relief image depends on the ambient temperature. The relief image can be erased thermically. It has been found, however, that the number of recording cycles which can be performed with photothermoplastics is limited.
It is also known to use recording materials with elastomeric layers, such as shown in German Offenlegungsschrift DE-OS 25 54 205 where the heating step is not required to render charge images visible. A photoconductive layer and an elastomer layer are present on a conductive support. The recording material is first uniformly charged electrostatically or provided with a flexible conductive layer to which a potential is applied. As long as image-wise distributed potential differences are maintained by exposure, the elastomer layer may be reversibly deformed into a relief image. A disadvantage of this process is the fact that the durability of the images is relatively short and does not sufficiently come up to practical requirements. Further, the multi-layer structure of the recording material is expensive.
Further, the Eidophor method is known for achieving a temporary, reversible deformation of a dielectric liquid (e.g., E. I. Sponable, JSMPTE 60, 1953, No. 4, 337). In this process a vacuum tube is utilized wherein an oil film on a conductive support is image-wise sprayed with charges by which surface deformations are produced. A disadvantage aspect of this procedure is that, due to a charge flow-off through the oil film, the relief image is of very short durability. As a consequence, continuous charge images are produced only on the oil film.